The semiconductor device fabrication process involves the etching step of treating members in a corrosive halogen-base gas plasma atmosphere. Members having sprayed coatings are known to be fully corrosion resistant in such atmosphere. For example, coatings are deposited on the surface of metallic aluminum and ceramic (typically aluminum oxide) substrates by atmospheric plasma spraying of yttrium oxide (Patent Documents 1 and 2) or yttrium fluoride (Patent Documents 3 and 4). Such sprayed members are used in the area of an etching system or etcher which comes in contact with the halogen-base gas plasma. Typical corrosive halogen-base gases used in the semiconductor device fabrication process are fluorine-base gases such as SF6, CF4, CHF3, ClF1 and HF and chlorine-base gases such as Cl2, BCl3 and HCl.
Yttrium oxide-deposited members obtained by plasma spraying of yttrium oxide suffer from few technical problems and have long been utilized as semiconductor-related sprayed members. When yttrium oxide-deposited members are used in the etching step with fluorine gas, there arises the problem that the etching step becomes unstable because outermost surface yttrium oxide can react with a fluoride at the initial of the step, and so the fluorine gas concentration within the etching system changes. This problem is known as “process shift.”
To overcome this problem, the replacement by yttrium fluoride-deposited members is under consideration. However, yttrium fluoride tends to have slightly weak corrosion resistance in a halogen-base gas plasma atmosphere, as compared with yttrium oxide. In addition, the yttrium fluoride sprayed coatings have many crevices on their surface and release many particles, as compared with the yttrium oxide sprayed coatings.
Under the circumstances, yttrium oxyfluoride having the characteristics of both to yttrium oxide and yttrium fluoride is regarded attractive as a spray material. Patent Document 5 discloses an attempt to use yttrium oxyfluoride. While yttrium oxyfluoride-deposited members are prepared by atmospheric plasma spraying of a yttrium oxyfluoride spray material, consistent deposition of yttrium oxyfluoride as a sprayed coating is difficult because oxidation gives rise to a compositional shift of fluorine depletion and oxygen enrichment, forming yttrium oxide.